In the H.264 video coding standard, it is possible to deblock a reconstructed/decoded picture (simply referred to as a decoded picture) for better display and also for better inter-picture prediction. In order to remove blocking artifacts in low bit-rate block-based video coding, a method (commonly called “in-loop deblocking filter”) is applied to smooth pixels, which are adjoining a block boundary. (See ITU-T and ISO/IEC JTC 1, “Advanced video coding for generic audiovisual services,” ITU-T Recommendation H.264 and ISO/IEC 14496-10 (MPEG4-AVC); ITU T Rec. H.264|ISO/IEC 14496-10 version 1 refers to the first approved version (2003) of this Recommendation|International Standard; ITU T Rec. H.264|ISO/IEC 14496-10 version 2 refers to the integrated text containing the corrections specified in the first technical corrigendum; ITU T Rec. H.264|ISO/IEC 14496-10 version 3 refers to the integrated text containing both the first technical corrigendum (2004) and the first amendment, which is referred to as the “Fidelity range extensions”; and ITU T Rec. H.264|ISO/IEC 14496-10 version 4 (the current specification) refers to the integrated text containing the first technical corrigendum (2004), the first amendment (the “Fidelity range extensions”), and an additional technical corrigendum (2005). In the ITU-T, the next published version after version 2 was version 4 (due to the completion of the drafting work for version 4 prior to the formal approval opportunity for a final of the version 3 text)).
The current draft of the new Annex G of the H.264 standard (referred to as the SVC standard) specifies a scalable coding extension, where additional layers are described for enhancing (spatially, temporally, and quality-wise) a basic H.264 coded bitstream. The decoded pictures of spatial and quality enhancement layers (hereinafter called enhancement layers) can also be deblocked using an in-loop process that is a simple modification of the basic H.264 deblocking process; this process is described in the SVC standard. (See T. Wiegand, G. Sullivan, J. Reichel, H. Schwarz, M. Wien, eds., “Joint Draft ITU-T Rec. H.264|ISO/IEC 14496-10/Amd.3 Scalable video coding,” Joint Video Team, Doc. JVT-X201, which is publicly available at the website ftp3.itu.int/av-arch/jvt-site/2007—06_Geneva/JVT-X201.zip, July 2007, and which is incorporated by reference herein in its entirety).
In the SVC standard deblocking process, each individual block (e.g., 4×4 or 8×8) of a picture is deblocked differently depending on how the individual block is coded. One of the coding parameters that affects deblocking is the quantization parameter (QP) used for the block. A lower QP indicates finer quantization of the coefficients representing the block pixels, and thus yields a better decoded representation of the original block. In the deblocking process, the QP of each block is used to derive the threshold values for deciding whether to deblock or not, and for determining how many boundary pixels to smooth out and by how much.
In the case where an enhancement layer block has no encoded information of its own and all information needed to decode the enhancement layer block is derived from its base layer block, which often happens when the enhancement layer block is encoded in higher QP than the base layer block, using the enhancement layer block's QP tends to smooth out more pixels than needed to address the boundary artifacts.
Consideration is now being given to improving processes for deblocking scalable-encoded video picture blocks, and in particular, enhancement layer blocks.